Process for producing nitrogen trichloride



May 7, l940 E. s'rAulzrr PROCESS FOR PRODUING NITROGEN TRICHLORIDE Filed June '222. 1937 llllluvllIl/f ATTORNEYS Patented May 7, 1940 uNiTgEn STATES PATENT ottica PROCESS FOR. PRODUCING NITROGEN TRICHLORIDE Netherlands Application June 22, 1937, serial No. 4149,787

' In the Netherlands June 30, 1936 7 Claims.

In my copending application Serial No. 51,714, filed November 26, 1935, now Patent No. 2,118,903 granted May 31, 1938, the preparation of nitrogen trichloride by the electrolysis of an acidined solu 6 tion containing ammonium and chloride ions has been described. In said application-it hasvbeen disclosed that by the electroylsis of water solutions of ammonium chloride, or other water solutions containing ammonium and chloride 10 ions, which have been given an acid reaction by the addition of acid, the production of nitrogen trichloride is favored and that the yield of nitrogen trichloride from the electrolysis of said acidined solutions increases as the acidity of the u solution increases. vIt has also been disclosed in said application that hydrochloric acid, as well` as other acids, may be added to the ammonium chloride solution, or other solution containing ammonium and chloride ions, to impart to the said solutions an acid, reaction, and that the quantity` of hydrochloric acid or other acid that is used per gram-molecule of ammonium chloride may fluctuate between broad limits, e. g., both with one-tenth and 2 gram-equivalents of acid per gram-molecule of ammonium chloride, good results have been obtained. During the electrolysis of said acid reacting solutionsI containing ammonium` and chloride ions, nitrogen trichloride is removed from the electrolyte by passing or blowing air or other gas through the electrolyte in the cell during electrolysis, or suction or vacuum is applied to the cell to produce a low or n decreased pressure of gas over the electrolyte whereby, in the latter instance also, the nitrogen trichloride is caused to escape from the electrolyte and enters the gases which are sucked or aspirated from the cell-by the suction apparatus or other apparatus 'producing the vacuum or partial vacuum. The nitrogen trichloride pre- 40 pared in this way can be used with advantage for improving the color and the baking quality of our, as well as for maturing our. The devices and apparatuses for the preparation of nitrogen trichloride in the electrolytic way described must accordingly be mounted in our mills when the nitrogen trichloride is usedfor the treatment of flour. Since the production of flour is, as a rule,

a continuous process, the electrochemical preparation of' nitrogen trichloride for the treatment of flour should preferably take place in such a way that it can be continued for a long period of time without interruption and without supervision and attendance being necessary.

In applying the process described in my above mentioned patent application, it appeared to be necessary to add a new or additional portion of acid from time to time to the electrolyte in order to maintain the acid reaction of the electrolyte, since the electrochemical process of preparing the nitrogen trichloride apparently took` place with 5 consumption of acid. However, handling acids and especially strong acids is extremely incon- Venient in works or plants, such as ilour mills', that are not equipped for handling acids. Moreover, it was of course a drawback of the said l0 process that a constant control of the degree of acidity of the electrolyte was necessary, since there was the danger that by omitting a timely addition of acid, the degree of acidity of the electrolyte would fall too much, so that even an lo alkaline reaction could arise, through which the production of nitrogen trichloride would be decreased to a very considerable extent and nally would ypractically cease altogetherf That the danger is not excluded that the re- 20 action of the electrolyte mayv really become an alkalineone, if care is not taken for a timely addition of acid, appears from the following table giving the results of the determinations of acid in an electrolyte that in the beginning of the ex.- 25 periment contained per one litre of -water solution (electrolyte)l 150 grams of ammonium chloride and 24 grams of hydrochloric acid (HC1). 'I'he electrolysis was carried out with a' current strength of 1.6 amp. at a tension of 3-3.5 volts. 3U The alterations in the degree of acidity of the electrolyte were as follows:

Grams of hydrochloric acid per 35 coms. of electrolyte Time cfelectrolysis, hours 'remo NGK oen-no Alk in It was now iound that it is possible to keep the acidity of the'water solution of ammonium chlo- 45 described in my said application continuously for long periods of time, with a constant or -nearly constant acidity, without extraneous addition of hydrochloric acid or other acid, by so adjusting or -regulatingthe amount of nitrogen trichloride that is allowed to decompose with the formation of acid that the amount of acid resulting from such decomposition of nitrogen trichloride will compensate or equal exactly. or approximately the amount of acid consumed in the. electrolysis of the acid reacting aqueous solution containing l Now according to the process of the present invention measures are taken, in accordance with 'v the above mentioned chemical reaction, to let the said acid forming reaction take place to the desired extent, so the electrolyte remains constant or nearly constant.

It appeared that the above mentioned reaction is influenced by various circumstances, so that it is to be considered that the extent to which the reaction takes place is determined by more than one factor.

In the first place, the concentration of the ammonium ions is of importance and this concentration must be as high as possible in order to iet the reaction take place to the right. Thus,

according to the process of the present invention, one preferably uses a concentrated ammonium chloride solution as the electrolyte; for example, a water solution of ammonium chloride containing grams of ammonium chloride per litre, but the upper limit of the concentration is fixed by the' solubility of ammonium chloride under the circumstances prevailing in the electrolyte. `It is clear that the ammonium chloride in the electrolyte may be wholly or'partly substituted by another ammonium salt, provided that a suiciently high chloride ion concentration is. provided in some other way.

It is further advisable to practice the process of the present invention at a temperature which is rnot too low, since the solubility of ammonium chloride increases' with rising temperature. Suitable temperatures lie, for example, between l5 and 35 C. If necessary the electrolyte is kept at the right temperature by heating or cooling.

A further measure that may be taken in order to attain the object contemplated by the present invention is the provision of a large volume of electrolyte. In this case the nitrogen trichloride that is present inA the electrolytein a dissolved state Aand in the form of gas bubbles nds an opportunity to reach the required degree of decomposition prior to escaping from the electrolyte as a gas. It appears that the best measure for the volume of electrolyte is the volume of electrolyte per square centimeter of active electrode surface. Dependent on the material that is used for the electrodesY this volume may lie at various values.

-'I'hus in case of graphite and carbon electrodes 5-100 ccms. of electrolyte is the volume per square centimeter of active surface of electrodes; and in case of platinum electrodes, the volume is 100-2000 ccms. per square centimeter of active 9,199,942 manner it becomes possible to practice the process electrode surface.

that the degree of acidity of h By active surface of electrodes is meant the total surface of both positiva and negative electrodes that-is taking part in the charging and discharging of ions during electrolysis.` y

Another manner of 4influencing theV degree of electrolyte, consists in the appropriate choice oi the quantity of air or of the other gas that is blown through the electrolyte during the elecdecomposition of the nitrogen trichloride accordj lng to the present invention, and accordingly for increasing the amount of available acid in the' trolysis according to my above mentioned application in order to eliminate the nitrogen trichloride. formed.

The iniiuence of the quantity of air is such that in case of a too small supply of air, the degree o f acidity of the electrolyte will rise because the period'of contact of the nitrogen trichloride with the electrolyte is too long in this case. If, on the contrary, the quantity of air is too large the time of contact ofthe nitrogen trichloride with the' electrolyte will be too small and the degree of acidity of the electrolyte will fall. .It was found that per 100 litres of electrolyte a current of 30-300 litres of air or other gas (measured at 15 C. and 760 mm. pressure) per minute gives the best results. It is, however, necessary to determine by some preliminary tests what quantity of air or other gas must be used inea certain case.-

Besides the quantity of air or other gas that is passed through the electrolyte during electrolysis,

the direction of movement of the air or gas in" the electrolyte is of importance. .The air may be given such a movement through the electrolyzing cell or electrolyte that the nitrogen trichloride formed remains in contact with the electrolyte for the required time prior to escaping. By this contact the above mentioned reaction of decomposition may take'place to the desired ex-r tent.

. As in theprocess described in my above mentioned application, the air or other gas used ac- 'cording to the present invention serves also as a means for eliminating the nitrogen trichloride formed from the electrolyte and as a stirring agent for keeping the composition of the ,electrolyte unifor-m.` The stirring movement of theair or other gas may be made such by an appropriate choice of the method of introduction. that the nitrogen trichloride formed at the electrodes, prior to leaving the liquid,'is`carried away by the current of air and is further brought into contact with the electrolyte. Various possibilities .exist for carrying out the above described form of stirring movement, some of which, by

wayof example, are illustrated in the accompany- I ing drawings, in which Figures 1, 2 and 4 respectively represent vertical cross sections of three different electrolyzing cells yand Figure 3 represents a top plan view of another electrolyzing cell. According to Figure l, for example, the air or gas may be blown into thel electrolytic'cell container I at the bottom, inthe neighborhood of the sidewalls, through perforated pipes 2 and 3,

and the electrodes-4 and Smay be mounted inthe middle of the cell between the two air supply pipes 2 and 3. In this way the air or other gas sets the liquid in a double rotating movement as is indicated by the broken lines 6' and arrow sides as shown in Figure 2. Referring said 'lol figure, the numeral II indicates the container of the electrolytic cell. Theair is blown into the cell at the bottom, near or at the middle, through a perforated pipe I2, and two sets of electrodes Il and I5 may be employed, one set being positioned near one side of the electrolytic cell and the other set being positioned near the opposite side of the electrolytic cell. 'I'he air orgas introduced causes the contents oi' the cell to be circulated as indicated, by the broken lines I6 and arrow heads I1. As is indicatedin Figure 2, in this case also the nitrogen trichloride formed at the electrodes is brought into contact with the electrolyte by the air or other gas.

Figure 3 illustrates another manner of carryingout the process according to which the electrolyte is'given a' horizontalv rotating movement in a cell container 2|, owing to a sidelong supply of air from perforated pipev 22. Thisvrotating movement of the electrolyte also causes the desired contact of nitrogen trichloride with the electrolyte. 'I'he electrodes in Figure 3 are designated by the numerals 24 and 25, and the move-- ment of the liquid contents of the cell isindicated by broken line 26 and arrow heads 21.

It is to be understood that mechanical stirrers may be used toy obtain the stirring or circulation of the contents of the electrolytic cell, although `of course this is less advisable from a construction or operating point of view than using the current of air in the Way described, especially since the air is blown through the electrolyte for removing nitrogen trichloride and for maintaining the body of the electrolyte uniform during electrolysis.

By mounting partition walls, edges, grooves and the like inthe electrolytic cell, the movement of air in the liquid may be caused to `take place in the desired manner, and theshape of the electrolyzing cell may be chosen to contribute to obtaining the desired movement oi' air or electrolyte. This manner of practicing the ini vention is illustrated in Figure 4. The cell container 3| is divided into two compartments of substantially equal volume by means of the partition 38, below which is positioned the perforated pipe 32 from which air is discharged along each side of the partition. Two sets o f electrodes 34 and 35 are provided, one set being placed near one side of the cell container and the other set being placed near the opposite side oi the cell container, there being one set of electrodes, as shown in the drawing, in each compartment of the cell. The air introduced from pipe 32 causes the contents of each compartment of the cell to be circulated as indicated by the broken lines 36 and arrow heads 31.

A combination of the various' methods for moving the liquid in the electrolytic cell with one or more of the other measures described above may be used, if only care is taken that the nitrogen trichloride formed is brought into contact with the electrolyte in such a way that a degree of decomposition takes place at which the degree of acidity oi the electrolyte remains constant ,or nearly constant. It is also to be understood that two or more orall of the above described measures for promoting the decomposition of nitrogen trichloride may be used at the same time in connection with the same electrolytic cell for compensating for losses of acid during the production o1 nitrogen trichloride as` described in my above mentioned application for patent.

' yPreliminary tests are'necessary to determine and its dimensions determine to what to be taken so that an arrangementy to what extent and in what way the measures described above must be lapplied. in each case, since the eilect cannot always exactly be calculated in advance. 'Ihe various measures infiuencing the decomposition of the nitrogen trichloride supplement each others action but not in such a way that a simple computation of their combined effect is possible. With each cell construction, in which also the shape of the cell play a part, somepreliminary tests under control of the degree of acidity of the electrolyte must be performed in order to extent the said measures are of said measures isreached which results in a constant or nearly constant degree of acidity of the electrolyte. If the electrolysis is continued in this arrangement, the degree of acidity of the electlyte will automatically remain at the same v ue.

It will be seen from the electrolysis to yield is removed from the said foregoing that an aqu'a `ous solution of acid reaction containing am` monium ions and chloride ions is subjected to solution during electrolysis thereof. for example, by passing air through said solution during elec-v trolysis thereof; that the acidity of the said solution is maintained constant or approximately constant during the electrolysis thereof by leaving enough of the nitrogen trichloride produced Aby the electrolysis in contact with the said solution for a suillcient period of time to react with 1t to form a suiiicient amount of acid to equal approximately equal or compensate the'amount of acid which is consumed in the electrolysis. In this manner, the loss or consumption of acid produced by the electrolytic action may be compensated or equalled, or even exceeded, according to the amount of nitrogen trichloride that is allowed to be decomposed by the electrolyte with the formation of acid. While the initial acid condition of the electrolyte or solution electrolyzed may be produced by the addition of acid. to the electrolyte', it is to be understood that this initial condition may be brought about in any other suitable way, for

example the initial acid condition may be pro; duced by allowing nitrogen trichloride to react withl an electrolyte containing ammonium chloride or ammonium and chloride ions.

I claim: l

1 In the art of producing nitrogen trichloride wherein an aqueous solution containing ammonium and chloride ions and free acid is electrolyzed, and nitrogen trichloride is removed from the solution, the process which comprises removing only a part of the electrolytically produced nitrogen trichloride from the solution and contacting the remaining part of the electrolytically produced nitrogen trichloride with the solution for sumcient time to be decomposed' thereby with the production of acid, theextent of said removal of nitrogen trichloride being such that the said remaining part oi' nitrogen trichloride so decomposed is suiiicient in amount to yield at least enough acid to equal the amount of freeacid consumed in the electrolysis.

2. In the art of'producing nitrogen trichloride wherein an aqueous solution containing am'- monium and chloride ions and free acid is electrolyzed, and nitrogen trichloride is removed from the solution by passage of a gas through the solution, the process which comprises removing only a part oi' the electrolytically produced nilns trogen trichloride from the solution by said gas and contacting the remaining part of the electrolytlcally produced nitrogen trichloride with the solution for sufiicient time to be decomposed thereby with the production of acid, the extent of said removal of nitrogen trichloride being such that the said remaining part of nitrogen trichloride so decomposed is sufficient in amount to yield enough acid to maintain the free acid content of the solution about constant.

3. In the art ofk producing nitrogen trichloride by the electrolysis oi an aqueous solution containing ammonium and chloride ions and free acid and in which a carrier gas for nitrogen trichloride is passed through the solution during the electrolysis, the process which comprises maintaining the freeA acid content of the said solution during said electrolysis about constant` by conducting the carrier gas through the said solution during electrolysis at a rate of 30 to 300 liters per minute per 100 liters of solution undergoing electrolysis.

4. Process for producing nitrogen trichloride which comprises electrolyzingan aqueous solution containing ammonium and chloride ions in the presence of free acid which imparts to the solution an acidity greater than the acidity of solutions consisting of ammonium chloride dissolved in water, and conducting a gas through the solution during the electrolysis thereof to remove nitrogen trichloride, said gas being oi such a through vthe solution nature that in its passage through the solution nitrogen trichloride is carried out o! the solution by said gas, n through said solution and the rate of its passage part of the nitrogen trichloride `produced in the electrolysis is contacted for suilicient time for` Ireaction with said solution for the production of acid that the acid thereby resulting at least equals in amount the acid 'consumed in the electrolysis. 10

the remaining portion of the nitrogen trichloride which has not undergone reaction with said solu-u tion being carried away by said gas.

5. Processaccording to claim 2 in whichthe volume oi the aqueous solution electrolyzed is at 15 least 5 cubic centimeters per square centimeter of active surface of electrodes.

6. Process according to claim 2 in which carbon electrodes are employed in the electrolysis of the aqueous solution, .and in which the volume l0 of the aqueous solution is 5 to-100 cubic centimeters per square centimeter of active surface of electrodes.

'7. Process according toclaim 2 in which platinum electrodes are employed in the electrolysis of the aqueous solution, and in which the volume of the aqueous solution'is 100 to 2000 cubic centimeters per square centimeter of .active surface of electrodes.-

the manner of conducting saidl gas l being such thatsumcient 5 

